The use of communications systems for the transfer of voice and data between and among locations has become widespread. The use of industry-wide standards and protocols has accelerated such use, as they allow the designers of communication systems in accordance with such standards to take comfort in knowing in advance that a particular level of performance can be realized. In addition, the use of components and systems utilizing such standards allows the specification of components and sub-systems to be simplified, since compliance with a particular standard eliminates the need for tailoring the system to accommodate a particular element's thereof characteristics, and can permit or facilitate the interchange of components from various sources without compatibility concerns.
Typical communication systems utilize timing and synchronization signals to control event timing and to allow the passage of data between the units in a coordinated manner. One of the interconnected units is typically designated as a master, with the remaining units designated as slaves. The master unit generates the timing signals which are coordinated, or slaved, to by the remaining units. In this manner a unitary, system-wide time base and synchronization protocol is established and maintained.
It is of course important that coordination and synchronization is maintained as the system grows or shrinks. In many applications the reconfiguration of a system is done by a skilled technician, having the ability to reconfigure the system as appropriate. Further, other systems allow the addition and deletion of slave units with automatic reconfiguration, improving the versatility of such systems and simplifying the reconfiguration process.
Time Division Multiplexing (TDM) is a particularly popular and well accepted transmission method for telephony systems. Some TDM standard protocols are known as ISDN/E1/T1. They provide a robust architecture but are most commonly used in rack-mounted systems or the like for point-to-point communications in which interconnections between, and communications among, more than two users or locations is not typically contemplated. In an E1/T1 type system, one of the interconnected units must be configured to provide the necessary timing and sync signals for the unit or units which follow. In addition, E1/T1 type systems cannot typically be used to enable selective communications between a plurality of communications units as may be required in a rail car communications system and the like.
Rail cars have adopted the use of communication systems utilizing microprocessors to control operational functions and passenger communications. Towards such ends, the communications units in each car must be interconnected. Such rail car communications systems, however, present system interconnection requirements which differ from many other systems, and particular do not typically permit E1/T1 protocol systems to be employed. In addition to a rail car system requiring a varying number of communications units as a train is assembled from individual cars, a particular car may be attached to an existing train or sequence of cars at either end thereof. In a similar manner, individual cars can be removed from a train and/or their location within a train shuffled. This dynamic reconfiguration places additional burdens on the communication system between the cars. The coupling and uncoupling of rail cars is typically accomplished by personnel not having the necessary technical training required to reconfigure the communication system to accommodate the new car, nor during normal train operations do they typically have the time or are they often even permitted access to the communications system. Even communications systems which have the capacity to automatically accept the addition or deletion of additional “slave” units are ill-equipped to accommodate the loss of a designated master unit.
It is accordingly a purpose of the present invention to provide a multiple unit communications system or network incorporating E1/T1 type architecture.
Another purpose of the present invention is to provide a communications system, such as a communications system utilizing the E1/T1 protocol, which allows a plurality of individual communications units to be interconnected and operated in a flexible manner, and without the need for manual reconfiguration.
Yet another purpose of the present invention is to provide a method and apparatus for the automatic mediation and assignment of a responsibility, such as timing and/or synchronization of communications units, between peer units in a multiple unit system, and particularly a communication system.
A further purpose of the present invention is to provide a method and apparatus for dynamically allocating master and non-master relationships among E1/T1 protocol communications units as they are joined to and separated from each other within a communications system.
Still another purpose of the present invention is to provide a multi-drop communications system utilizing E1/T1 type architecture in which communications between units may be controlled by a parent unit, wherein communications are passed from or to the parent and a plurality of child units.